1. Green synthesis of Zeolitic Imidazolate Frameworks and their evaluation for ▫$CO_2$▫ capture in humid conditions : dissertationAljaž Škrjanc, 2024, doctoral dissertation Abstract: Emissions of green-house gasses have been in the forefront of scientific research in recent decades. One of the approaches towards reducing the amount of green gas CO2 in the atmosphere is its capture and storage with subsequent conversion where pure enough CO2 can be regenerated. While CO2 capture widely utilizes two mature technologies, amine absorption and cryogenic distillation, they both have significant downsides, in either cost or potential new danger to the environment. To that end an adsorption-based CO2 capture has seen quite a lot of interest in recently. Nanoporous materials have been extensively studied for this application, starting with zeolites, followed by aluminophosphates and also the new members of the porous materials group, the so called reticular porous materials. Metal-Organic Frameworks (MOFs), the first discovered reticular porous materials have shown very promising results for post combustion CO2 capture and recently also for in-door and direct air capture. MOFs are in general enough thermally stable for CO2 capture, their main weakness for wide applicability is sometimes lower selectivity for CO2 in real gas mixtures and lower stability in humid conditions.
Zeolitic imidazolate frameworks (ZIFs), a subgroup of MOFs, have in recent years been extensively studied for sorption applications, also CO2, due to their superior stability and kinetics for vapour/gas adsorption if compared to carboxylate-based MOFs. While extensively studied, an overview of articles shows that most research is limited to a limited set group of frameworks, with ZIF-8 being used in more than half of ZIF papers. While ZIF-8 has successfully been prepared in water and even in solvent-free conditions, the rest of the ZIFs synthesis still heavily rely on solvothermal synthesis with formamide based solvent systems and synthesis times upwards of 5 days. Even in the case of ZIF-8, while greener synthesis approaches are available, dimethylformamide (DMF) synthesis still prevails in the cases tested for CO2 capture, mainly due to the increased CO2 uptake resulting from the synergistic contribution of the remaining DMF solvent in the pores.
The goal of this thesis was to develop green synthesis approaches, both solvothermal and mechanochemical, for known ZIFs and then to extend the scope towards preparation of new ZIF materials. The goal for latter was to experimentally determine the optimal topology and functionality of ZIFs for CO2 adsorption in humid conditions. Model humid gas isotherms were developed and measured for a series of ZIFs with mostly SOD (sodalite) and RHO framework topologies and Zn and Ni as metal nodes. Finally, some novel bio-based binder materials were tested for the use with ZIFs.
The sorption tests revealed than the SOD topology ZIFs have high potential for CO2 sorption applications, as the adsorption is rapid and further combination of terminally functionalised imidazoles in those frameworks drastically increases the frameworks affinity for CO2 at lower pressures. With most common 4,5- functionalised imidazole having hydrophilic functional groups, the challenge of competitive water sorption still remains. On the other hand some hydrophobic 4,5-substituted sodalite ZIFs, both with 4,5-dichloroimidazole, show excellent CO2 sorption and even complete hydrophobicity. The results led us to hypothesize that further research on ZIFs- for CO2 capture has to shift form 2 substituted sodalite frameworks to 4,5 substituted frameworks with strongly dipolar hydrophobic groups. The hydrophilic polar groups currently in use lead to issues with competitive water adsorption, due to their potential to form hydrogen bonds with water. Furthermore, some new agar and alginate based shaping methods were tested, as both potential binders are not environmentally toxic and are already used on the industrial scale world-wide for other applications.
Keywords: carbon capture, synthesis, metal-organic frameworks, zeolitic imidazolate frameworks, nanoporous materials, dissertations
Published in RUNG: 10.09.2024; Views: 380; Downloads: 14
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2. Multi-layer palladium diselenide as a contact material for two-dimensional tungsten diselenide field-effect transistorsGennadiy Murastov, Muhammad Awais Aslam, Simon Leitner, Vadym Tkachuk, Iva Plutnarová, Egon Pavlica, Raul D. Rodriguez, Zdeněk Sofer, Aleksandar Matković, 2024, original scientific article Abstract: Tungsten diselenide (WSe2) has emerged as a promising ambipolar semiconductor material for field-effect transistors (FETs) due to its unique electronic properties, including a sizeable band gap, high carrier mobility, and remarkable on–off ratio. However, engineering the contacts to WSe2 remains an issue, and high contact barriers prevent the utilization of the full performance in electronic applications. Furthermore, it could be possible to tune the contacts to WSe2 for effective electron or hole injection and consequently pin the threshold voltage to either conduction or valence band. This would be the way to achieve complementary metal–oxide–semiconductor devices without doping of the channel material.This study investigates the behaviour of two-dimensional WSe2 field-effect transistors with multi-layer palladium diselenide (PdSe2) as a contact material. We demonstrate that PdSe2 contacts favour hole injection while preserving the ambipolar nature of the channel material. This consequently yields high-performance p-type WSe2 devices with PdSe2 van der Waals contacts. Further, we explore the tunability of the contact interface by selective laser alteration of the WSe2 under the contacts, enabling pinning of the threshold voltage to the valence band of WSe2, yielding pure p-type operation of the devices.
Keywords: field-effect transistor, tungsten diselenide, van der Waals, two-dimensional materials
Published in RUNG: 29.05.2024; Views: 926; Downloads: 6
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3. Fluorescent covalent organic frameworks : promising bioimaging materialsChimatahalli Santhakumar Karthik, Tina Škorjanc, Dinesh Shetty, 2024, original scientific article Abstract: Fluorescent covalent organic frameworks (COFs) have emerged as promising candidates for imaging living cells due to their unique properties and adjustable fluorescence. In this mini-review, we provide an overview of recent advancements in fluorescent COFs for bioimaging applications. We discuss the strategies used to design COFs with desirable properties such as high photostability, excellent biocompatibility, and pH sensitivity. Additionally, we explore the various ways in which fluorescent COFs are utilized in bioimaging, including cellular imaging, targeting specific organelles, and tracking biomolecules. We delve into their applications in sensing intracellular pH, reactive oxygen species (ROS), and specific biomarkers. Furthermore, we examine how functionalization techniques enhance the targeting and imaging capabilities of fluorescent COFs. Finally, we discuss the challenges and prospects in the field of fluorescent COFs for bioimaging in living cells, urging further research in this exciting area.
Keywords: covalent organic frameworks, fluorescent materials, imaging, bioimaging, biosensors
Published in RUNG: 05.03.2024; Views: 1251; Downloads: 6
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5. Uncovering the nature of transient and metastable nonequilibrium phases in 1T − ▫$TaS_2$ ▫Tanusree Saha, Arindam Pramanik, Barbara Ressel, Alessandra Ciavardini, Fabio Frassetto, Federico Galdenzi, Luca Poletto, Arun Ravindran, Primož Rebernik Ribič, Giovanni De Ninno, 2023, original scientific article Abstract: Complex systems are characterized by strong coupling between different microscopic degrees of freedom. Photoexcitation of such materials can drive them into new transient and metastable hidden phases that may not have any counterparts in equilibrium. By exploiting femtosecond time- and angle-resolved photoemission spectroscopy, we probe the photoinduced transient phase and the recovery dynamics of the ground state in a complex material: the charge density wave (CDW)–Mott insulator 1T-TaS2. We reveal striking similarities between the band structures of the transient phase and the (equilibrium) structurally undistorted metallic phase, with evidence for the coexistence of the low-temperature Mott insulating phase and high-temperature metallic phase. Following the transient phase, we find that the restorations of the Mott and CDW orders begin around the same time. This highlights that the Mott transition is tied to the CDW structural distortion, although earlier studies have shown that the collapses of Mott and CDW phases are decoupled from each other. Interestingly, as the suppressed order starts to recover, a metastable phase emerges before the material recovers to the ground state. Our results demonstrate that it is the CDW lattice order that drives the material into this metastable phase, which is indeed a commensurate CDW–Mott insulating phase but with a smaller CDW amplitude. Moreover, we find that the metastable phase emerges only under strong photoexcitation (∼3.6 mJ/cm2) and has no evidence when the photoexcitation strength is weak (∼1.2 mJ/cm2).
Keywords: angle resolved photoemission, time resolved photoemission, 2D materials, charge density wave, Mott insulator
Published in RUNG: 15.01.2024; Views: 1412; Downloads: 6
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6. Crystallizing covalent organic frameworks from metal organic framework through chemical induced-phase engineeringAbdul Khayum Mohammed, Safa Gaber, Jesus Raya, Tina Škorjanc, Nada Elmerhi, Sasi Stephen, Pilar Pena-Sánchez, Felipe Gándara, Steven Hinder, Mark A. Baker, Kyriaki Polychronopoulou, Dinesh Shetty, 2023, original scientific article Abstract: The ordered porous frameworks like MOFs and COFs are generally constructed using the monomers through distinctive metal-coordinated and covalent linkages. Meanwhile, the inter-structural transition between each class of these porous materials is an under-explored research area. However, such altered frameworks are expected to have exciting features compared to their pristine versions. Herein, we have demonstrated a chemical-induction phase-engineering strategy to transform a two dimensional conjugated Cu-based SA-MOF (Cu-Tp) into 2D-COFs (Cu-TpCOFs). The structural phase transition offered in-situ pore size engineering from 1.1 nm to 1.5–2.0 nm. Moreover, the Cu-TpCOFs showed uniform and low percentage-doped (~ 1–1.5%) metal distribution and improved crystallinity, porosity, and stability compared to the parent Cu-Tp MOF. The construction of a framework from another framework with new linkages opens interesting opportunities for phase-engineering.
Keywords: metal organic framework, covalent organic framework, phase engineering, chemical transformation, porous materials
Published in RUNG: 10.11.2023; Views: 1814; Downloads: 7
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7. Non-contact and self-calibrated photopyroelectric method for complete thermal characterization of porous materialsMohanachandran Nair Sindhu Swapna, Carmen Tripon, Robert Gutt, Alexandra Farcas, Marcel Bojan, Dorota Korte, Irina Kacso, Mladen Franko, Dorin Dadarlat, 2023, original scientific article Keywords: photopyroelectric calorimetry, thermal parameters, porous materials
Published in RUNG: 04.08.2023; Views: 1874; Downloads: 5
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8. Giant and tunable out-of-plane spin polarization of topological antimonenePolina M. Sheverdyaeva, Conor Hogan, Gustav Bihlmayer, Jun Fujii, Ivana Vobornik, Matteo Jugovac, Asish K. Kundu, Sandra Gardonio, Zipporah Rini Benher, Giovanni di Santo, 2023, original scientific article Keywords: density functional theory, spin-resolved ARPES, electronic structure, topological insulators, 2D materials, antimonene
Published in RUNG: 18.07.2023; Views: 1531; Downloads: 5
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10. Infrared spectra in amorphous alumina : a combined ab initio and experimental studyLuigi Giacomazzi, Nikita S. Shcheblanov, Mikhail E. Povarnitsyn, Yanbo Li, Andraž Mavrič, Barbara Zupančič, Jože Grdadolnik, Alfredo Pasquarello, 2023, original scientific article Abstract: We present a combined study based on the experimental measurements of an infrared (IR) dielectric function and first-principles calculations of IR spectra and the vibrational density of states (VDOS) of amorphous alumina (am−Al2O3). In particular, we show that the main features of the imaginary part of the dielectric function ε2(ω) at ∼380 and 630 cm−1 are related to the motions of threefold-coordinated oxygen atoms, which are the vast majority of oxygen atoms in am-Al2O3. Our analysis provides an alternative point of view with respect to an earlier suggested assignment of the vibrational modes, which relates them to the stretching and bending vibrational modes of AlOn (n=4, 5, and 6) polyhedra. Our assignment is based on the additive decomposition of the VDOS and ε2(ω) spectra, which shows that (i) the band at ∼380cm−1 features oxygen motions occurring in a direction normal to the plane defined by the three nearest-neighbor aluminum atoms, i.e., out-of-plane motions of oxygen atoms; (ii) Al-O stretching vibrations (i.e., in-plane motions of oxygen atoms) appear at frequencies above ∼500cm−1, which characterize the vibrational modes underlying the band at ∼630cm−1. Aluminum and fourfold-coordinated oxygen atoms contribute uniformly to the VDOS and ε2(ω) spectra in the frequency region ∼350–650 cm−1 without causing specific features. Our numerical results are in good agreement with the previous and presently obtained experimental data on the IR dielectric function of am−Al2O3 films. Finally, we show that the IR spectrum can be modeled successfully by assuming isotropic Born charges for aluminum atoms and fourfold-coordinated oxygen atoms, while requiring the use of three parameters, defined in a local reference frame, for the anisotropic Born charges of threefold-coordinated oxygen atoms.
Keywords: dielectric properties, microstructure, amorphous materials, density functional calculations, infrared techniques, aluminium oxide
Published in RUNG: 10.05.2023; Views: 1932; Downloads: 9
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